Expert: James Ball - 12/15/2010

Question
QUESTION: Here is my question.

I am installing a fireplace insert in my existing masonry fireplace/chimney.
I am trying to figure out if the hearth in front of my firebox is all brick or some frame covered with brick.
Is it a framed out box with bricks mortared to the box or is it all brick stacked up sitting on the subfloor?
If it is all brick then the k and r values i am trying to achieve will be far exceeded because it would literally be 1 foot of brick,
but if it is just a box covered in brick it would be cutting it close as only being 1 brick on its side.
This is a question/concern as part of the insert will be on the hearth and the insert requires specific R/K values for transferring heat.
My house was built in the late seventies. When in the basement under the fireplace I see that there is floor/framing reinforcement.
There is also mortar that has seeped through probably during construction which is leading me to believe that it is all brick.

Anyone with any help on this would be appreciated.

ANSWER: Hello Steve, most times that is a Hearth Extension and the frame it and then pour cement over that frame and build up from there, yours seems to be about 6-10" tall? not sure what was done underneath, maybe take some measurements on how far it sticks out and then check that in the basement? Check you insert for clearance to combustibles in front (you might have to put some thing on the floor out into the room and this should be lined to the top and insulated. check with your local building department
James

---------- FOLLOW-UP ----------

QUESTION: Hi James,
The hearth extension is 1 ft high and about 1ft extension from the fireplace opening. I have all my requirements. Have put full insulated liner and I will be putting down another foot of hearth extension on the floor using micore, durock and tile, that will put me past the required 18 in clearance. I have my permit and have passed all code just awaiting final inspections. I am just a being extra cautious about the hearth so if it is cement with brick on top I am just trying to make sure that would be sufficient.

Answer
Welcome back Steve, it sounds like you are one of the first  people to have every ting right that I did not have to fight with to help them be safe, good for you.
it sounds like the hearth extension will work find for what you need it to (double check by hitting it with a hammer and see if it sounds hollow?) but you should be good to go.
good luck
Happy Holidays
James